S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt and a process for production thereof

ABSTRACT

An S,S-ethylenediamine-N,N&#39;-disuccinic acid iron alkali salt which contains a lactam compound represented by the following general formula (1):wherein M is an ammonium ion or an alkali metal ion, and an ethylenediaminemonosuccinic acid represented by the following general formula (2):wherein M is an ammonium ion or an alkali metal ion, in an amount of 7 wt % or less, respectively.

This is a continuation of prior application Ser. No. 09/530,275, filedApr. 28, 2000, now U.S. Pat. No. 6,300,510 B1, which is herebyincorporated herein by reference in its entirety, which was the nationalphase of international application PCT/JP98/104917, filed Oct. 30, 1998,which designated the U.S. but was not published English.

TECHNICAL FIELD

The present invention relates to an S,S-ethylenediamine-N,N′-disuccinicacid iron alkali salt that is a chelate compound usable as aphotographic bleaching agent, a fertilizer or the like and has littleundesirable influence on the environment because of its goodbiodegradability, and a process for producing said salt.

BACKGROUND ART

The present inventors have disclosed in JP, 8-34764,A that anS,S-ethylenediamine-N,N′-disuccinic acid iron ammonium salt, which is acompound useful for photographic bleaching and the like, has a highbiodegradability. However, in a production process for producing thedisclosed compound, it was necessary to obtain a highly viscous andhighly slurry concentrate because of the very high solubility of thedesired compound, in order to obtain the desired compound in high yield.Therefore, there has been a desire for a production process having ahigher productivity as an industrial production process. A process forobtaining the desired compound by a concentration to dryness or acontinuous hot gas drying has achieved an improvement in the yield buthas been disadvantageous in product quality that, for example, powdersobtained by said process were so poor in shelf stability that it wascolored or was deteriorated in solubility.

Unlike a production process using an inorganic salt such as ironsulfate, a production process using iron oxide was expected to make itpossible to obtain a desired compound having a relatively high purity byevaporating a reaction solution to dryness as it was, unless startingmaterials are decomposed. However, when a meso/racemic mixture ofethylenediamine-N,N′-disuccinic acid was used, a product obtained bysuch a process had a very high hygroscopic in some cases and moreoverits purity was not sufficient. In addition, also whenS,S-ethylenediamine-N,N′-disuccinic acid was used, the resulting solidhad a low stability, for example, it was colored or gave an insolublematerial with a lapse of time. Furthermore, the solid had a low purityand the mass balance of the S,S-ethylenediamine-N,N′-disuccinic acidused was markedly unsatisfactory.

An object of the present invention is to solve such problems and providean S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt having ahigh storage stability and a process for producing the same in highyield.

DISCLOSURE OF THE INVENTION

The present inventors have made extensive studies in order to achievethe above object and consequently found that anS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt contains animpurity that is difficult to detect even under HPLC analysis conditionsunder which a slight amount of a chelate compound can be analyzed,because the impurity has a much lower chelate ability than that of othercomponents. Additionally, the present inventors found that, as a resultof various analyses such as mass spectrometry and NMR, the impurity is acompound derived from S,S-ethylenediamine-N,N′-disuccinic acid by aformation of a lactam ring. The present inventors also found that acoloring and a deterioration of a shelf stability of theS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt are due to thepresence of a compound of the following general formula (1) or acompound of the following general formula (2) as reaction by-productsand due that an iron complex's stability of these compounds is low thatthe compounds release a chelated iron with a lapse of time. Thus, thepresent inventors found that a reduction of an amount of the reactionby-products is important.

(Wherein M is an ammonium ion or an alkali metal ion.)

(Wherein n is an ammonium ion or an alkali metal ion.)

In addition, the present inventors found that even if these compoundsare contained in the S,S-ethylenediamine-N,N′-disuccinic acid ironalkali salt, this salt is not seriously deteriorated in shelf stabilitywhen a content of each of the compounds is 7 wt % or less. The presentinventors further found the following: a formation of these impuritiescan be inhibited by properly controlling a reaction temperature, areaction period of time and pH at the reaction and adding a reducingagent; of the impurities formed, the lactam compound is easily solublein a lower alcohol while the S,S-ethylenediamine-N,N′-disuccinic acidiron alkali salt is insoluble therein, and therefore only the impuritycan be dissolved by utilizing a difference in solubility between theimpurity and the lactam compound; and when a continuous hot gas dryingmethod is adopted, a decomposition ofS,S-ethylenediamine-N,N′-disuccinic acid during an oxidation can beminimized, and an oxidation of ferrous iron easily proceedssimultaneously with drying. Thus, the present invention has beenaccomplished.

That is, one aspect of the present invention is directed to anS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt which containsa lactam compound represented by the general formula (1) shown below andan ethylenediaminemonosuccinic acid represented by the general formula(2) shown below in an amount of 7 wt % or less, respectively:

wherein M is an ammonium ion or an alkali metal ion,

wherein M is an ammonium ion or an alkali metal ion,

Another aspect of the present invention is directed to a process forproducing the above-mentioned S,S-ethylenediamine-N,N′-disuccinic acidiron alkali salt.

BEST MODE FOR CARRYING OUT THE INVENTION

S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salts as such arestable at a room temperature and have a very high water-solubility of 60g/50 g H₂O or more, and aqueous solutions thereof are weakly acidicsubstances having a pH of about 5 and can be stably stored.

On the other hand, S,S-ethylenediamine-N,N′-disuccinic acid used as astarting material in a process for producing anS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt by an ironchelating reaction, is an unstable compound in an acidic solution. Itundergoes a lactam ring formation reaction or is decomposed by an amineelimination reaction. Additionally, this compound has a strong acidityof pH 2 or thereabout in an aqueous solution. Therefore, the compoundfurther characterized in that its cyclization gradually proceeds whenwater is present, without an addition of an acidic substance, even atroom temperature. The formation of a cyclization product and a fumaricacid, and a ethylenediaminemonosuccinic acid by an elimination reactionof amine are accelerated by heating.

However, a chelating reaction of iron under basic conditions results inan extreme decrease of a reactivity of iron oxide and a formation of alarge amount of iron hydroxide and iron ammine complexes. In addition,when the S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt isobtained in the form of powder, an alkali present in excess undesirablycaused a moisture absorption to deteriorate a stability of a product.Therefore, the reaction was unavoidably carried out with heating in aweakly acidic pH region of 3 to 6, so that the above-mentionedby-products were formed. Furthermore, since these by-products, i.e. thecyclization product and the by-products produced by the amineelimination reaction, have a lower chelate ability than that ofS,S-ethylenediamine-N,N′-disuccinic acid, they released iron ions, owingto a pH change, a composition change of liquid caused by additives, anda lapse of time, so that a water-insoluble iron hydrate was formed tocause an appearance of turbidity in an aqueous solution.

The present inventors found the following: an appearance of theturbidity can be prevented to such an extent that it does not cause anyproblem in practice, by reducing a content of each of theabove-mentioned by-products to 7 wt % or less; and the content of eachof the by-products can be reduced to 7 wt % or less by taking thecountermeasure described below. Thus, the present invention has beenaccomplished.

Since a formation of the decomposition products and the cyclizationproduct is dependent on a temperature at a chelating reaction of iron oriron oxide with S,S-ethylenediamine-N,N′-disuccinic acid, a reactionperiod of time and pH at the reaction, a desired compound containingonly a slight amount of the by-products can be obtained by making theseconditions suitable and adding a stabilizer.

S,S-ethylenediamine-N,N′-disuccinic acid used in the process of thepresent invention can be synthesized by a known process. For example,this compound can be synthesized either by reacting 1,2-dihaloethanewith L-aspartic acid with heating in the presence of an alkali metalhydroxide (Inorganic Chemistry, 7 (11), 2405 (1968)) or by utilizing amicrobial enzyme.

As an alkali used in the present invention, ammonia and alkali metalsconventionally used in S,S-ethylenediamine-N,N′- disuccinic acid ironalkali salts are preferable. Alkaline earth metals and organicmonoamines such as alkylamines may be used as the alkali.

As an iron oxide used in the process of the present invention, any ofmagnetite, goethite and hematite and the like may be used in the form ofpowder, magnetite being the most preferable and hematite being thesecond most preferable. When hematite is used, hematite having aspecific surface area of 10 (m²/g) or more, more preferably 15 (m²/g) ormore, in terms of BET value is preferable. When magnetite is used,magnetite having a specific surface area of 5 (m /g) or more, morepreferably 6 (m²/g) or more, in terms of BET value is preferable. Whengoethite is used, goethite having a specific surface area of 85 (m²/g)or more, more preferably 95 (m²/g) or more, in terms of BET value ispreferable. Here, the term “BET value” means a specific surface areavalue measured by a low-temperature N₂ gas adsorption.

As to the order of charging of starting materials in the process of thepresent invention, either a method comprising charging an aqueous mediumand S,S-ethylenediamine-N,N′-disuccinic acid in a reactor and thenadding thereto iron oxide powder, or a method comprising charging anaqueous medium and iron oxide powder in a reactor and then addingthereto S,S-ethylenediamine-N,N′-disuccinic acid may be adopted, thelatter being more preferable. As the aqueous medium, either a water oran alcohol-containing water may be used, a water being preferably used.

In the method of charging an aqueous medium and iron oxide powder in areactor and then adding thereto S,S-ethylenediamine-N,N′-disuccinicacid, a dispersion liquid obtained from the aqueous medium and the ironoxide powder is heated at from 70 to 100° C., preferably from 75 to 95°C., more preferably from 80 to 90° C., andS,S-ethylenediamine-N,N′-disuccinic acid or anS,S-ethylenediamine-N,N′-disuccinic acid monoalkali salt is continuouslyor intermittently added thereto in the form of powder or a dispersion orsolution in an aqueous medium. In this case, pH of the reaction mixtureis preferably maintained at from 4.5 to 7, more preferably from 5 to 6.

More particularly, S,S-ethylenediamine-N,N′-disuccinic acid used ismixed with an aqueous alkali solution containing an alkali in an amountof from equivalent to 1.4 moles, preferably from 1.05 to 1.25 moles, permole of S,S-ethylenediamine-N,N′-disuccinic acid, to obtain a dispersionliquid or aqueous solution of an S,S-ethylenediamine-N,N′-disuccinicacid alkali salt, which is continuously or intermittently added to theiron oxide dispersion liquid. It is also possible to add theS,S-ethylenediamine- N,N′-disuccinic acid powder and the aqueous alkalisolution to the iron oxide dispersion liquid separately and continuouslyor intermittently without beforehand mixing them, to carry out thereaction. In this case, when an addition rate ofS,S-ethylenediamine-N,N′-disuccinic acid is rapider than that of theaqueous alkali solution, pH is lowered. Therefore, it is preferable tocarry out the reaction while adjusting the pH by adding the aqueousalkali solution so that the pH may be always in a range of 4.5 to 7.Although depending on a reaction temperature, a period of time requiredfor the addition may be properly selected in a range of from 0.2 to 4hours, preferably from 1 to 3 hours.

Furthermore, a formation of a cyclization product can be inhibited byadding a reducing agent at the time of the chelating reaction. Specificexamples of the reducing agent are inorganic reducing agents in the formof powder, wire, ribbon or the like of a metal such as iron powder, zincpowder, magnesium powder, aluminum powder, etc.; and organic reducingagents such as ascorbic acid, isoascorbic acid, oxalic acid, etc. Ironis preferable for suppressing a contamination of a product withimpurities. The amount of such additives is 0.1-20 mol %, preferablyapproximately 1-10 mol %, based on the amount ofS,S-ethylenediamine-N,N′-disuccinic acid.

When hematite or goethite is used as the iron oxide, a small amount of adivalent iron exists in a reaction mixture obtained by a dissolution ofthe iron oxide and a chelation. When magnetite is used, a divalent ironexists in the reaction mixture in an amount of from a few % to over ten% based on the total amount of iron existing in the reaction mixture.For oxidizing the divalent iron into a trivalent iron, a molecularoxygen can be used. When a desired composition is obtained as powder, itis not necessary to introduce a molecular oxygen into the reactionmixture to carry out an oxidation reaction and then dry it which are theconventional procedure. Insoluble materials are removed from theabove-mentioned reaction mixture, if necessary, by filtering thereaction mixture and a residue is dried by the use of a continuous hotgas dryer. The divalent iron is effectively oxidized by an airintroduced during the drying. Moreover, since a treatment period of timeis short, a decomposition of S,S-ethylenediamine-N,N′-disuccinic acid,which has occurred when an air blows into, is inhibited. Therefore,powder of a desired composition can be efficiently obtained. Thecontinuous hot gas dryer includes, for example, a spray dryer and acontinuous granulation dryer. A temperature of the hot gas used rangesfrom 70° C. to 200° C.

S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt reactionmixture containing of the compounds represented by the above generalformula (1) and (2) in an amount of more than 7% is reduced in watercontent or allowed to assume a dried state, and then the treatedreaction mixture is washed with a water-containing lower alcohol,whereby S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt havingintended low contents of the compounds of the general formula (1) and(2) can be efficiently obtained. Examples of the lower alcohol describedabove include lower alcohols of 1 to 4 carbon atoms. Specific examplesthereof include methyl alcohol, ethyl alcohol, isopropyl alcohol,n-propyl alcohol, isobutyl alcohol, tert-butyl alcohol, etc.

Specifically, a water contained in theS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt reactionmixture containing high contents of the by-products is allowed toevaporate by a concentration under a reduced pressure of the reactionmixture until the water content becomes 60% or less based on the amountof solid components. Then, an absolute or water-containing lower alcoholis added to the residue so as to form a water-containing lower alcoholhaving a water content of 3 to 35%, preferably 5 to 20%, wherebycrystals are dispersed. By separating the crystals by filtration,S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt having acontent of each of the above-mentioned by-products of not more than 7%can be easily obtained.

Another treatment method is as follows: after the reaction mixture isdried with a continuous hot gas dryer, as in spray drying, driedsubstances can be washed either by dispersing it in a water-containingalcohol having a water content of 3 to 35%, preferably 5 to 20%,followed by a separation by filtration, or by charging the driedsubstances into a Buchner funnel or the like and rinsing the driedsubstances with the water-containing alcohol, whereby anS,S-ethylenediamine- N,N′-disuccinic acid iron alkali salt having acontent of each of the above-mentioned by-products of not more than 7%can be easily obtained.

The present invention is illustrated in further detail with thefollowing examples and comparative examples, which should not beconstrued as limiting the scope of the invention.

Iron yield and analysis methods for iron component and a chelatecomponent are as follows.

Iron yield=[(the amount of iron dissolved as determined by atitration)/(the total amount of all iron atoms used in thereaction)]×100

Analysis method for iron component:

All ions of dissolved iron in a sample is converted to ferric iron ionsand the thus treated sample is reacted with potassium iodide and thentitrated with sodium thiosulfate by using a starch as an indicator.

Analysis method for a chelate component:

An aqueous sodium hydroxide solution is added to an iron complex toeliminate the iron therefrom, and then the resulting substance isdissolved in a solution containing copper to form a copper complex,which is analyzed by a liquid chromatography (column: ODS-2, wavelength:254 nm, eluent: a buffer solution containing copper, analysistemperature: 40° C.).

EXAMPLE 1

146 g of S,S-ethylenediamine-N,N′-disuccinic acid, 300 g of water and 21g of 98% sodium hydroxide were charged in a reactor equipped with astirrer and a thermometer, and were stirred and mixed at roomtemperature. 37.7 g of magnetite having a BET value of 6.5 (m²/g) and1.4 g of iron powder were added thereto, and a reaction was carried outwith heating and thorough stirring at 80° C. for 2 hours. The contentsof by-products in the reaction mixture were as follows: the content of acyclization product having a lactam ring was 2.7%, and the content of adeamined ethylenediaminemonosuccinic acid was 2%. Insoluble materialswere removed from the obtained reaction mixture by filtration, and thenthe residue was adjusted to pH 5 withS,S-ethylenediamine-N,N′-disuccinic acid. The thus obtained liquid,after a completion of the pH adjustment, was dried with a spray dryer toobtain an S,S-ethylenediamine-N,N′-disuccinic acid iron sodium saltcomposition having a lactam ring content of 2.5% and anethylenediaminemonosuccinic acid content of 2%, with an iron yield of98%.

EXAMPLES 2 to 10

Table 1 shows results obtained by carrying out the reaction in the samemanner as in Example 1 except for changing the stabilizer.

TABLE 1 Mono- Examples Lactam succinic and ring acid Iron ComparativeKind of content content yield Examples Base Stabilizer [%] [%] [%]Example 2 Potassium Iron powder 2.6 2 98 Example 3 Ammonium Iron powder2.6 2 97 Example 4 Sodium Magnesium 3.1 2 97 Example 5 AmmoniumMagnesium 3.0 2 96 Example 6 Sodium Ascorbic 2.9 2 97 acid Example 7Ammonium Ascorbic 3.1 2 97 acid Example 8 Sodium Oxalic acid 2.9 2 97Example 9 Ammonium Oxalic acid 2.9 2 98 Example 10 Ammonium Formic acid6.5 5.4 93 Comparative sodium None 11 9 90 Example 1

COMPARATIVE EXAMPLE 1

A reaction and after-treatment were carried out under the sameconditions as in Example 1 except for adding no stabilizer. Table 1shows the results obtained.

EXAMPLE 11

A liquid, after a completion of pH adjustment, which had been obtainedin Comparative Example 1 was concentrated under a reduced pressure untilits water content became 60 wt % based on the weight of theS,S-ethylenediamine-N,N′-disuccinic acid iron sodium salt produced.Methanol of 2, 3 times volume as much as the water contained in theresulting residue was slowly added to the resulting concentrated liquidresidue with thoroughly stirring. After a completion of the addition ofmethanol, the resulting liquid was stirred as it was for 1 hour, andcrystals precipitated were filtered and then dried to obtainS,S-ethylenediamine-N,N′-disuccinic acid iron sodium salt in a yield of80%. In this case, a content of a cyclization product having a lactamring (a lactam ring content) was 0.5%, and a content of anethylenediaminemonosuccinic acid was 0.2%.

EXAMPLE 12

One part by weight of a spray-dried S,S-ethylenediamine-N,N′-disuccinicacid iron alkali salt product obtained in Comparative Example 1 wasdispersed in 2 parts by volume of ethanol containing 20 vol % of water,and the resulting dispersion was stirred at room temperature for 60minutes. Then, crystals were separated by filtration and dried to obtainS,S-ethylenediamine N,N′-disuccinic acid iron alkali salt containing 2%of a cyclization product having a lactam ring and 1.5% of anethylenediaminemonosuccinic acid, in a yield after purification of 80%.

EXAMPLES 13 and 14

Reaction was carried out by the same procedure as in Example 1 exceptfor using goethite having a BET value of 95 (m²/g), or hematite having aBET value of 18 (m²/g), in place of the magnetite having a BET value of6.5 (m²/g) . Table 2 shows the results obtained.

COMPARATIVE EXAMPLES 2 to 4

Reaction was carried out by the same procedure as in Example 1 exceptfor using goethite having a BET value of 80 (m²/g), or hematite having aBET value of 9 (m²/g), in place of the magnetite having a BET value of6.5 (m²/g) . Table 2 shows the results obtained.

TABLE 2 Examples Lactam Monosuccinic and ring acid Iron Comparative BETcontent content yield Examples Kind of Iron value [%] [%] [%] Example 1Magnetite 6.5 2.5 2 98 Example 13 Goethite 95 4.9 3 95 Example 14Hematite 18 4.5 2 96 Comparative Magnetite 4.5 10 6 90 Example 2Comparative Goethite 80 12 9 70 Example 3 Comparative Hematite 9 10 7 88Example 4

EXAMPLE 15

Each of the powders obtained in Examples 1, 10 and 13 and ComparativeExamples 1 and 3 was dissolved to obtain a 40% aqueous solution. Thesolution was stored at 50° C. for 1 week and then diluted to 1% and thedissolution state of the resulting diluted solution was observed. Whenthe crystals obtained in any of Comparative Examples were used,insoluble materials were found. In contrast, when the crystals obtainedin any of Examples were used, no insoluble material was found.

EXAMPLE 16

200 g of water, 40 g of magnetite (iron content: 70.5%) and 3 g of ironpowder were charged in a 1-liter cylindrical flask equipped with astirrer, a thermometer and a material feed opening, and were heated at85° C. Then, 146 g of S,S-ethylenediamine-N,N′-disuccinic acid wasdispersed in 365 g of water containing 10.2 g of ammonia, and theresulting dispersion liquid was added to an iron oxide dispersionliquid, which had been beforehand prepared, over about 2 hours by theuse of a slurry pump while maintaining a mixture temperature at 80 to85° C. During the addition, pH of the reaction mixture graduallydecreased from 7 and varied in a range of 5.5 to 6. After a completionof the addition, the reaction mixture was maintained at 80° C. for 30minutes and then cooled to room temperature. This reaction mixturecontained a cyclization product having a lactam ring formed in an amountof only 0.5% based on the amount of S,S-ethylenediamine-N,N′-disuccinicacid used and divalent iron ions in an amount of 10% based on the totalamount of all iron ions.

Subsequently, insoluble components were removed from the obtainedreaction mixture by filtration, and 7g ofS,S-ethylenediamine-N,N′-disuccinic acid was added to the liquid residueto adjust the amounts of iron ions andS,S-ethylenediamine-N,N′-disuccinic acid to equimolar. Then, theresulting mixture was dried with a spray dryer to obtain 193 g of anS,S-ethylenediamine-N,N′-disuccinic acid iron ammonium salt containing0.5% of a compound having a lactam ring and 0.2% of anethylenediaminemonosuccinic acid, and having a content of divalent ironions of 0.5% based on all iron ions, and a purity of 98% or more.

EXAMPLE 17

200 g of water, 40 g of magnetite (iron content: 70.5%) and 3 g of ironpowder were charged in a 1-liter cylindrical flask equipped with astirrer, a thermometer and a material feed opening, and were heated at80° C. Then, 146 g of S,S-ethylenediamine-N,N′-disuccinic acid was addedthereto with a spoon over 2.5 hours while maintaining a mixturetemperature at 80 to 85° C. During the addition, 150 g of an aqueoussolution containing 20.4 g of sodium hydroxide was added to the reactionmixture while adjusting pH of the reaction mixture to 5 to 6. After acompletion of the addition, the reaction mixture was maintained at 80°C. for 15 minutes and then cooled to room temperature. The reactionmixture contained a cyclization product having a lactam ring formed inan amount of only 0.4% based on the amount ofS,S-ethylenediamine-N,N′-disuccinic acid used. After divalent iron ionsremained in an amount of about 8% based on the total amount of all ironions were oxidized by bubbling air into the reaction mixture, insolublematerials were removed by filtration.

The amount of a compound having a lactam ring in theS,S-ethylenediamine-N,N′-disuccinic acid iron sodium salt aqueoussolution thus obtained was 0.4% based on the amount ofS,S-ethylenediamine-N,N′-disuccinic acid used.

EXAMPLE 18

200 g of water and 40 g of magnetite (iron content: 70.5%) were chargedin a 1-liter cylindrical flask equipped with a stirrer, a thermometerand a material feed opening, and were heated at 85° C. Then, 146 g ofS,S-ethylenediamine- N,N′-disuccinic acid was dispersed in 365 g ofwater containing 10.2 g of ammonia, and the resulting dispersion liquidwas added to an iron oxide dispersion liquid, which had been beforehandprepared, over 2 hours by the use of a slurry pump while maintaining amixture temperature at 80 to 85° C. During the addition, the pH of thereaction mixture gradually decreased from 7 and varied in a range of 5.5to 6. After a completion of the addition, the reaction mixture wasmaintained at 80° C. for 30 minutes and then cooled to room temperature.Divalent iron ions remained in the reaction mixture in an amount ofabout 10% based on the total amount of all iron ions were oxidized bybubbling air into the reaction mixture, and then insoluble materialswere removed by filtration. In the solution thus obtained, a cyclizationproduct having a lactam ring was formed in an amount of 0.9% based onthe amount of S,S-ethylenediamine-N,N′-disuccinic acid used.

COMPARATIVE EXAMPLE 5

200 g of water, 40 g of magnetite (iron content: 70.5%) and 3 g of ironpowder were charged in a 1-liter cylindrical flask equipped with astirrer, a thermometer and a material feed opening, and were heated at80° C. Then, 146 g of S,S-ethylenediamine-N,N′-disuccinic acid was addedthereto with a spoon over about 2.5 hours while maintaining a mixturetemperature at 80 to 85° C. During the addition, 150 g of an aqueoussolution containing 20.4 g of sodium hydroxide was added to the reactionmixture while adjusting pH of the reaction mixture at from 3.0 to 4.0,and the whole aqueous sodium hydroxide solution prepared was added atlast. After a completion of the addition, the reaction mixture wasmaintained at 80° C. for 15 minutes and then cooled to room temperature.In this reaction mixture, a cyclization product having a lactam ring wasformed in an amount of 2.1% based on the amount ofS,S-ethylenediamine-N,N′-disuccinic acid used.

INDUSTRIAL APPLICABILITY

The S,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt of thepresent invention is a chelate compound usable as a photographicbleaching agent, a fertilizer or the like, and has little undesirableinfluence on the environment because of its good biodegradability.

What is claimed is:
 1. A composition comprisingS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt in an amountof 86 wt % or more but less than 100 wt %, a lactam compound in amountof more than 0 wt % but 7 wt % or less represented by the followinggeneral formula (1):

wherein M is an ammonium ion or an alkali metal ion, and anethylenediaminemonosuccinic acid in amount of 7 wt % or less representedby the following general formula (2):

wherein M is an ammonium ion or an alkali metal ion.
 2. The compositionaccording to claim 1, wherein the alkali salt in theS,S-ethylenediamine-N,N′-disuccinic acid iron alkali salt is an ammoniumsalt or an alkali metal salt.
 3. The composition according to claim 1,wherein the lactam compound is present in an amount of at least 0.4 wt.%.
 4. The composition according to claim 1, wherein the amount ofethylene diaminemonosuccinic acid is present in an amount of at least0.2 wt. %.
 5. A photographic bleaching composition comprising acomposition according to claim
 1. 6. A fertilizer comprising acomposition according to claim 1.